ardav's main problem seems to surround probable cause. Clearly, there is enough information here where the police can arrest him for the crime. While I don't think this would be a valid search incident as it is not a normal custodial arrest, I agree with CdwJava that if ardav decided to NOT show the police ID they could bring him in and book him for failure to identify rather than cite and release.
Now, the burden is on the state/municipality to prove beyond a reasonable doubt the elements of the crime. Does ardav have a shot? This thread has gone round and round and I have no idea. Personally, I suspect all the facts certainly lead a reasonable man to think he did have alcohol in the cup (Dumping, he had recently drunk alcohol and might have been under the influence, the cup previously contained alcohol.), but proof beyond a reasonable doubt? ardav seems to want to make it an equation where either the strut supports or fails. Most people know that is not the way it works. People never have all the facts and they make inferences on the facts not known. I bet I know the inferences the judge will make on these facts.